Machines comprising rotating parts generally require seal units to prevent the entry of moisture and contaminants into e.g. a bearing that supports the rotating part, and to prevent the leakage of grease that lubricates the bearing. Radial lip seals are one example of a commonly used seal. The seal has a contact lip that bears against a counterface, which ensures effective sealing under static conditions. Under dynamic conditions, the lip is in sliding contact with the counterface, which generates friction and heat, meaning that conventional lip seals are often unsuitable for use at high rotational speeds.
One application where effective sealing is important under static conditions and at high speeds is in the field of railway bearings. In compact Traction Bearing Units, for example, which operate at speeds over 200 km/hr, excessive friction and heat generation would quickly lead to wear and early seal failure. Consequently, non-contact labyrinth seals are sometimes employed in such bearing units. An example is disclosed in U.S. Pat. No. 8,356,941. A drawback of labyrinth seals, however, is that they may not provide effective sealing under static conditions, unless the gaps between opposing labyrinth surfaces are very small. The tolerance requirements in such sealing arrangements are therefore stricter.
Consequently, there is room for improvement.